Electrical interconnects exhibit limitations in scaling to even higher bandwidth density in tern-s of the maximum data rate per line, the interconnect distance, power and crosstalk. Optical interconnects may overcome these limitations. Parallel opto-electronic modules exist that transform several electrical signals into optical signals or vice-versa. However, the currently available modules are large in their size and the interconnect density at the electrical side is limited to the density that is available in standard printed circuit board technology. In order to enable optical technology to emerge in areas very close to the processor, the interconnect density between the processor and the optical module will have to be increased.
In SCM or MCM technology, the processor or switch chip is mounted onto a carrier substrate. This carrier does exhibit a large interconnect density and serves several functions. First it offers a high density interconnect between electronic components mounted on the carrier surface. Furthermore, the carrier is the interconnect medium between the processor(s) and the printed circuit board (PCB). In order to utilize the high interconnect density potential of optical technology, the optoelectronic elements have to be attached to the carrier substrate. Several approaches to bring optics to the SCM or MCM are described in the prior art.
In U.S. Pat. No. 6,512,861 B2 by Intel, the optoelectronic package is mounted on to the printed circuit board with embedded optical waveguides and a mirror is used to redirect the light.
In U.S. Pat. No. 6,611,635 B1 by Fujitsu, a variety of embodiments are disclosed where either a mirror is used to redirect the light, or the opto-electronic element is directly connected to the waveguide.
U.S. Pat. No. 6,439,895 B1 by Intel describes a socket compatible with optical and electrical interconnects in that it has an opening in the center to let optical signals pass through.
U.S. Published Patent Application No. 2006/0078248 A1 by NEC describes an opto-electronic package where the alignment between the board and the optical waveguides is achieved through pins.